JP2003123752A - Composite electrode material, method of manufacturing the same, and composite electrode using composite electrode material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite electrode material superior in high reversible capacity and filling characteristic, and suitably used as an electrode material for a lithium ion battery and an electrochemical super capacity. SOLUTION: In this composite electrode material prepared by coating a surface of a conductive material having an average particle size of primary particles of 10-60 nm, and a specific surface area by nitrogen adsorption of 50-300 m<2> /g, with metallic oxide capable of absorbing and desorbing lithium, the conductive material is carbonaceous material, and the metallic oxide is the oxide of at least one kind of metal selected from the metals belonging to a range of the fourth to the sixth cycle and the groups 3 to 12 in the periodic table.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composite electrode material suitable for use as an electrode material for lithium ion batteries, electrochemical supercapacitors and the like, a method for producing the same, and a composite electrode using the composite electrode material.

[0002]

_2. Description of the Related Art An electrode of a lithium-ion battery, especially a positive electrode, is prepared by dispersing a powder of a positive electrode active material such as LiCoO ₂ and a conductive material such as carbon into a binder solution prepared by dissolving a binder in an organic solvent or a binder dispersed in water. To prepare a positive electrode mixture-containing paste, apply the positive electrode mixture-containing paste to a current collector made of metal foil, etc., and dry it to form a thin film positive electrode on the current collector. It is manufactured through the step of forming the mixture layer.

However, the lithium ion battery having the positive electrode manufactured as described above has a high energy density, but since the positive electrode active material is originally an insulator, it is charged and discharged under high current density (under high load). However, there is a problem in that a high capacity cannot be obtained.

Further, studies have also been conducted on electrochemical supercapacitors utilizing the oxidation-reduction reaction of lithium, aiming at higher output by finely dividing the active material and mixing a large amount of conductive materials. However, when finely divided, the active material becomes bulky (bulk), and the conductive material is also generally bulky, so that the filling property of the electrode is deteriorated and a high energy density cannot be obtained. there were. Further, if the filling property is poor, a gap is generated between the active material and the conductive substance, and the contact property is not always good, so that there is a problem that sufficient conductivity cannot be secured.

Therefore, the present inventors have proposed a novel composite electrode material in which a conductive material is coated with a metal oxide capable of inserting and releasing lithium (Japanese Patent Application No. 2000-
269531). This composite electrode material is obtained by adding a conductive substance to a colloidal solution of the above metal oxide and subjecting it to heat treatment, and also has a high electrode filling property, and since it is compounded with a conductive substance, it has high output characteristics. It has the feature of indicating.

[0006]

The above-mentioned composite electrode material is
Since the metal oxide capable of inserting and removing lithium and the conductive material are combined, the utilization rate of the metal oxide, which is the active material, is improved, and the discharge capacity that is almost the theoretical value is secured. It is possible to

However, taking the case of using vanadium pentoxide as the metal oxide, the discharge capacity when using a crystalline body of vanadium pentoxide is at most 200.
It is mAh / g, and at present, the discharge capacity when using the amorphous material is about 360 mAh / g. This is not enough to meet the recent market demand for higher capacity.

The present invention provides lithium which exhibits a high discharge capacity even under a high current density, and has a high reversible capacity which greatly exceeds the theoretical capacity of the active material, while maintaining the advantage that the composite electrode material has a high filling capacity. It is an object to provide a composite electrode material suitable for use as an electrode material for ion batteries, electrochemical supercapacitors and the like.

[0009]

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, regarding a conductive substance coated with a metal oxide, the average particle size of primary particles thereof is 10 to 60 nm. And has a specific surface area of 5 due to nitrogen adsorption
By using a conductive substance having a content of 0 to 300 m ² / g, particularly a carbonaceous material, it is possible to significantly improve the theoretical capacity of a metal oxide capable of electrochemically inserting and removing lithium. I found it.

That is, in the composite electrode material of the present invention, lithium is inserted into the surface of a conductive substance having an average primary particle size of 10 to 60 nm and a specific surface area of 50 to 300 m ² / g due to nitrogen adsorption. -Characterized by being coated with a metal oxide capable of being desorbed.

In the composite electrode material of the present invention, it is preferable that the conductive substance is a carbonaceous material. This is because the carbonaceous material has excellent conductivity and is lightweight.

In the composite electrode material of the present invention, the metal oxide is at least one kind selected from metals belonging to groups 4 to 6 and groups 3 to 12 of the periodic table. It is preferable that the metal oxide is. This is because these metal oxides are excellent in lithium insertion and desorption characteristics.

The method for producing a composite electrode material according to the present invention comprises: a conductive material having an average particle size of primary particles of 10 to 60 nm and a specific surface area of 50 to 300 m ² / g by nitrogen adsorption; Is mixed with a colloidal solution of the above-mentioned metal oxide capable of being inserted and removed, and then heated. As a result, a strong metal oxide film can be formed on the surface of the conductive substance.

Further, the composite electrode of the present invention is characterized by using the composite electrode material.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION First, an embodiment of the composite electrode material of the present invention will be described. The metal oxide used in the composite electrode material of the present invention is an oxide of a metal belonging to the fourth to sixth periods of the periodic table and within the groups of the third to twelfth groups. Specifically, for example, Sc, Ti, V, Cr, M
n, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb,
Mo, Tc, Ru, Pd, Ag, Cd, lanthanoid,
Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg
And oxides of metals such as V, Cr, Mn,
Preferred are oxides of metals such as Fe, Co, and Ni that belong to groups 5 to 10 of the fourth period of the periodic table, and complex metal oxides containing at least one of these metals.

The conductive substance used in the composite electrode material of the present invention has an average primary particle size of 10 to 60 nm and a specific surface area of 50 to 300 m ² / g due to nitrogen adsorption.
The material is not particularly limited as long as it is a conductive substance, but a carbonaceous material is substantially preferably used. Specifically, for example, carbon black, atomized amorphous carbon, carbon fiber, natural graphite or artificial graphite can be used.

It is necessary that the average particle diameter of the primary particles of the above-mentioned conductive material is within the range of 10 to 60 nm. That is, good conductivity is imparted by setting the average particle diameter to 10 nm or more. On the other hand, in order to obtain a composite electrode material which is coated with a metal oxide over a wide range and exhibits a high reversible capacity that greatly exceeds the theoretical capacity of the active material, the average particle diameter of the conductive material is reduced to 60 nm or less, It is necessary to increase the specific surface area to 50 m ² / g or more.
However, even if the average particle diameter is within the above range, the specific surface area is 300 m ^{2 as} long as most of the specific surface area originates from pores (micropores) of less than 2 nm, such as activated carbon.
However, since the colloidal solution of the metal oxide does not penetrate into the micropores, it is difficult to effectively coat the metal oxide, and it is difficult to achieve the object of the present invention. Can not. Therefore, the conductive material is
It is necessary that the average particle size of the primary particles is 10 to 60 nm and the specific surface area due to nitrogen adsorption is within the range of 50 to 300 m ² / g.

Here, the average particle diameter of the conductive material is
From the photograph taken by the scanning electron microscope (SEM) 1
This is the average of 000 particles selected and the particle diameters measured. The specific surface area is B due to nitrogen adsorption.
It is measured by the ET method.

Next, an embodiment of the method for producing the composite electrode material of the present invention will be described. Incidentally, the conductive substance and the metal oxide used in the method for producing the composite electrode material of the present invention,
The description is omitted because it is the same as that described in the embodiment of the composite electrode material of the present invention.

In the production method of the present invention, the metal oxide is made into a colloidal solution and then mixed with the conductive substance.
The mixing ratio of the metal oxide and the conductive substance is preferably 70:30 to 10:90 in terms of mass ratio, and particularly 50:
50 to 25:75 is more preferable. This is because if it is within this range, good discharge capacity and conductivity can be secured.

The preparation of the colloidal solution of the metal oxide is
Usually, it is difficult to directly convert the metal oxide itself into a colloidal solution, so either mix the metal powder with a solution containing an oxidizing agent such as hydrogen peroxide, or use metal acetate, nitrate, carbonate, etc. Is preferably mixed with a solution containing an oxidizing substance to prepare.

When mixing and dispersing the colloidal solution of the metal oxide and the conductive substance, a stirrer,
Any mixing means such as a ball mill and ultrasonic dispersion can be adopted. Further, the temperature and time during the mixing are not particularly limited, but are, for example, 0 to 40.
It is preferable to mix and disperse at a temperature of about 1 to 12 hours.

The heat treatment after mixing and dispersing may be carried out after the mixture of the metal oxide and the conductive substance is separated from the dispersion liquid to some extent by filtration, centrifugation or the like, or the mixed dispersion liquid is used as it is. You may go. The conditions for this heat treatment are not particularly limited, but the temperature is preferably 50 ° C. or higher, more preferably 80 ° C. or higher, and 450
C. or lower is preferable, and 300.degree. C. or lower is more preferable. Especially when a carbonaceous material is used as the conductive substance, 4
If the temperature exceeds 50 ° C, an oxidative decomposition reaction of carbon occurs. Therefore, it is preferable to perform the heat treatment at a temperature lower than that in the case of using the metal powder, and more preferable to perform the heat treatment at 300 ° C or lower. The heating time is preferably 1 hour or longer, more preferably 3 hours or longer, and is preferably 24 hours or shorter, more preferably 10 hours or shorter.

The composite electrode material comprising the composite of the metal oxide and the conductive substance obtained through the above heat treatment has a bulkiness larger than that of the mixed powder obtained by simply mixing the metal oxide and the conductive substance. It is low, and when expressed in bulk (bulk) density,
It has a high bulk density and excellent filling properties as an electrode material. That is, the bulk density is the density including the space existing between the individual powders when the powders are filled in the container without vibrating, and the mass that can be filled in a predetermined volume is divided by the value of the volume. Can be determined by The higher the value of the bulk density, the lower the bulk of the powder, which means that the composite electrode material of the present invention has excellent filling properties. However, since this bulk density has different preferable values when the metal oxide and the conductive substance are different, it cannot be generally determined which range is preferable, but according to the present invention, the bulk density of the composite electrode material is The true density can be increased to about ½.

To manufacture an electrode using the composite electrode material of the present invention obtained as described above, a binder such as polytetrafluoroethylene or polyvinylidene fluoride is added to the composite electrode material and mixed to obtain an electrode. The electrode mixture thus obtained may be molded by an appropriate means. For example, the electrode mixture is pressure-molded, or the electrode mixture is dispersed in a solvent to prepare an electrode mixture-containing paste.

When preparing this electrode mixture-containing paste, the binder may be dissolved in a solvent in advance and then mixed with the composite electrode material. Then, the obtained electrode mixture-containing paste is applied to a current collector made of a metal foil, a metal net, or the like, and dried to form a thin film electrode mixture layer, whereby an electrode is produced.

However, the method for producing the electrodes is not limited to the above-exemplified method, and other methods may be used. For example,
The electrode may be prepared by applying the mixed dispersion liquid of the colloidal solution of the metal oxide and the conductive substance on one or both sides of a current collector similar to the above, and then performing heat treatment.
In addition, an appropriate amount of an aqueous dispersion of polytetrafluoroethylene was added to a mixed dispersion of the colloidal solution of the above metal oxide and a conductive substance, mixed to form a paste, and the paste was applied to a current collector, followed by heat treatment. You may produce an electrode by doing.

Since the composite electrode material of the present invention has a function of doping / dedoping lithium ions, it can be used as an electrode material for lithium ion batteries, electrochemical supercapacitors and the like. In particular, since the composite electrode material of the present invention exhibits a high discharge capacity even under a high current density,
It is suitable as an electrode material for lithium-ion batteries and electrochemical supercapacitors as a driving power source for applications requiring high output such as electric vehicles and electric bicycles.

The composite electrode material of the present invention is composed of a composite of an oxide of a metal and a conductive substance, which belong to the fourth to sixth periods of the periodic table and within the range of the third to twelfth periods. However, other substances may be contained within a range that does not adversely affect the characteristics, and by such an added substance,
It can be expected to improve safety and cycle characteristics.

When the composite electrode material of the present invention was observed with a transmission electron microscope (TEM), black contours which were not seen in the conductive substance alone were present on the surface of the particles, and the energy dispersive X It was confirmed by a line microanalyzer that the black contours were metal oxides. Therefore, it is considered that the composite electrode material of the present invention has a structure in which the surface of the particles of the conductive substance is covered with the metal oxide film. The thickness of the metal oxide coating is 0.5 to 1
It is preferably 0 nm. If the thickness is less than 0.5 nm, the active material layer becomes thin accordingly, so that a sufficient discharge capacity cannot be obtained, and if it exceeds 10 nm, the thickness of the active material layer becomes too large and the conductivity decreases, resulting in sufficient output characteristics. Can't get

Further, in the present invention, the expression of the composite electrode material may be expressed as a composite in which the surface of a conductive substance is coated with a metal oxide. This means that the material and the conductive substance may be formed as raw materials, and does not necessarily mean that the metal oxide and the conductive substance are all reacted and integrated. That is, in the composite electrode material, it is considered that most of the metal oxide and the conductive substance remain unchanged without any change.
It is considered that some of them may react with each other by the heat treatment to be integrated.

[0032]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only those examples.

Example 1 1 g of metallic vanadium and 30 substances
100% of hydrogen peroxide water of volume%³And mix in an ice bath for 3
Stir and mix for hours. Leave this for 24 hours at room temperature
Vanadium iodide (V ₂O_Five) Was obtained as a colloidal solution
It was

Obtained vanadium pentoxide (metal oxide)
0.1 g of carbon black (conductive substance) having an average particle diameter of 23 nm determined by SEM and a specific surface area of 133 m ² / g determined by the BET 5-point method by nitrogen adsorption, in 2 g of water, Acetone (1 g) was added, and the mixture was stirred for 3 hours with a stirrer, mixed and dispersed to obtain a dispersion liquid.

Next, the above dispersion liquid was applied onto an aluminum foil having a thickness of 15 μm using an applicator. The coating amount was 2 mg / cm ² . Then, it heat-processed at 120 degreeC for 5 hours, and obtained the composite electrode of this invention. The mass ratio of vanadium pentoxide to carbon black in this composite electrode was 7:10.

Example 2 A composite electrode of the present invention was obtained in the same manner as in Example 1, except that acetylene black having an average particle size of 40 nm and a specific surface area of 70 m ² / g was used as the conductive substance.

Comparative Example 1 A composite electrode of Comparative Example was obtained in the same manner as in Example 1 except that acetylene black having an average particle size of 70 nm and a specific surface area of 32 m ² / g was used as a conductive substance. .

Comparative Example 2 A composite electrode of Comparative Example was prepared in the same manner as in Example 1 except that a phenol resin-based activated carbon having an average particle size of 25 μm and a specific surface area of 2500 m ² / g was used as a conductive substance. Obtained.

The composite electrodes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were punched out into a circle having a diameter of 10 mm, and these were used as working electrodes, and the counter electrode had a thickness of 1 mm and a diameter of 17 m.
m of disc-shaped lithium was used, and an electrolyte prepared by dissolving 1 mol / dm ³ of LiPF ₆ in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was used. A coin-shaped lithium battery having a diameter of 20 mm and a height of 1.6 mm was produced.

This battery is charged with a charge cut voltage of 4.2.
V and discharge cut voltage were 2.0 V, and a charge / discharge test was performed at a high current density of 1 mA / cm ² to measure the discharge capacity after the initial discharge. The results are shown in Table 1. Here, the discharge capacity means the discharge capacity corresponding to the mass of the metal oxide contained in the composite electrode material.

[0041]

[Table 1]

When vanadium pentoxide in an amorphous form is discharged up to 2 V with respect to a lithium electrode, lithium can be inserted up to X = 2.5 as Li _X V ₂ O ₅ . That is, its theoretical capacity is estimated to be 360 mAh / g. As is clear from the results shown in Table 1, in Examples 1 and 2 using the composite electrode of the present invention, 400 m exceeding the theoretical capacity.
A discharge capacity of Ah / g or more could be obtained. On the other hand, Comparative Example 1 using acetylene black having a large average particle diameter and small specific surface area has a lower discharge capacity than Examples 1 and 2, and Comparative Example 2 using activated carbon having a high specific surface area has a lower discharge capacity. became.

[0043]

As described above, when the composite electrode material of the present invention is used, a high discharge capacity is exhibited even under a high current density, and the advantage that the filling property is excellent is maintained, while the theoretical capacity of the active material is greatly exceeded. It is possible to provide a lithium-ion battery, an electrochemical supercapacitor, or the like that exhibits a high reversible capacity.

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Claims (5)

[Claims] 1. The average particle size of primary particles is 10 to 60 nm.
And has a specific surface area of 50 to 300 m ² due to nitrogen adsorption.
A composite electrode material characterized in that the surface of a conductive substance having a weight ratio of / g is coated with a metal oxide capable of inserting and releasing lithium. 2. The composite electrode material according to claim 1, wherein the conductive substance is a carbonaceous material. 3. The metal oxide is an oxide of at least one kind of metal selected from metals belonging to groups 4 to 6 and groups 3 to 12 of the periodic table. The composite electrode material according to claim 1 or 2. 4. The average particle diameter of primary particles is 10 to 60 nm.
And has a specific surface area of 50 to 300 m ² due to nitrogen adsorption.
/ G of a conductive substance and a colloidal solution of a metal oxide capable of inserting and releasing lithium are mixed and then heated, which is a method for producing a composite electrode material. 5. A composite electrode using the composite electrode material according to claim 1.